RxNorm is a widely used drug terminology developed at the National Library of Medicine (NLM). Use cases include e-prescription and exchange of drug information. For example, use of RxNorm is required by the Meaningful Use incentive program, for medication reconciliation and in clinical quality measures. As part of our research and development activities at the Lister Hill National Center for Biomedical Communications (LHNCBC), we have created various methods for mapping drug formularies to RxNorm and have integrated RxNorm with other sources (NDF-RT, ATC, DrugBank). RxNorm is distributed as a relational database. In order to facilitate its adoption and use, we have developed a graphical user interface (RxNav), as well as heavily used application programming interfaces (APIs) for RxNorm and companion resources (RxTerms, NDF-RT). We also developed methods for assessing the quality of RxNorm and related resources (NDF-RT, ATC, DrugBank). Finally, we have used RxNorm and other drug resources in applications including cohort selection, daily dose assessment, medication identification in text, and extraction of adverse drug events from MEDLINE indexing. The RxNorm API also supports retrieval of drug information through MedlinePlusConnect.